Preheat oven to 180c. In a large bowl cream butter, vanilla and sugar together until sugar has dissolved. Add in egg and beat until combined. Add in cashew nuts, flour and milk together and combine. Fold in Rice Bubbles, then drop a dessertspoon of the mixture onto a baking tray lined with glad bake. Flatten biscuit slightly and cook until golden brown for around 20 minutes at oven temperature of 150c.